1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device and a method of manufacturing the same, particularly to a semiconductor integrated circuit device having a memory cell including a magnetoresistive effect device and a method of manufacturing the semiconductor integrated circuit device.
2. Description of the Related Art
A magnetoresistive random access memory (hereafter referred to as MRAM) is one of memories for writing or reading data by electricity or magnetism.
FIG. 48A is a top view showing a typical MRAM, FIG. 48B is a sectional view taken along the line 48B—48B in FIG. 48A, and FIG. 48C is a sectional view taken along the line 48C—48C in FIG. 48A.
As shown in FIGS. 48A to 48C, there are a first galvanomagnetic-field wiring 101 extending in the first direction X and a second galvanomagnetic-field wiring 102 extending in the second direction Y crossing the first direction X. A magnetoresistive effect device 103 is set to the crossing portion between the first galvanomagnetic-field wiring 101 and the second galvanomagnetic-field wiring 102. A TMR device including magnetic tunnel junction (Tunneling MagnetoResistive; hereafter referred to as TMR) is generally used for the magnetoresistive effect device 103. The magnetoresistive effect device 103 is hereafter referred to as a TMR device 103.
The TMR device 103 is selected by selecting the first and second galvanomagnetic-field wirings 101 and 102 one each and thereby, data is read from or written in the TMR device 103 of an optional bit. Specifically, data is read by selecting a pair of first and second galvanomagnetic-field wirings 101 and 102 and detecting the magnitude of the current circulating between the selected first and second galvanomagnetic-field wirings 101 and 102.
Moreover, data is written by selecting a pair of first and second galvanomagnetic-field wirings 101 and 102 and supplying a current between the selected first and second galvanomagnetic-field wirings 101 and 102. Furthermore, by using the fact that a magnetic field generated by the current becomes strong at the crossing portion between the selected first and second galvanomagnetic-field wirings 101 and 102, data is written in the TMR device 103 located at the crossing portion.
In the case of a typical MRAM, the width WY-WL of the first galvanomagnetic-field wiring 101 is larger than the width WY-TMR along the second direction Y of the TMR device 103 and the width WX-BL of the second galvanomagnetic-field wiring 102 is larger than the width WX-TMR along the first direction X of the TMR 103. This is because the TMR device 103 is worked through the photolithography. In the case of the photolithography, misalignment of a mask occurs. The value of misalignment is approx. tens of nanometers at present.
To work the TMR 103 so that it is not shifted from the crossing portion between the first galvanomagnetic-field wiring 101 and the second galvanomagnetic-field wiring 102, it is necessary to add an alignment allowance MY considering a displacement of the TMR device 103 to the width WY-WL. Similarly, an alignment allowance MX is added to the width WX-BL.
The above condition causes a trouble when forming a larger memory by reducing the cell size of the MRAM for one bit.
Moreover, a magnetization reversal threshold value Hsw is one of device parameters of the MRAM. The magnetization reversal threshold value Hsw is the intensity of a magnetic field when reversal of the direction of the spin of a ferromagnetic material is started and one of parameters for deciding the intensity of a magnetic field to be applied to the TMR device 103 when data is written.
When the fluctuation band of the magnetization reversal threshold value Hsw is too large, data may be erroneously written. The magnetization reversal threshold value Hsw is fluctuated depending on the shape of the TMR device 103. Therefore, to manufacture the MRAM, it is important to control the magnetization reversal threshold value Hsw, particularly to minimize the fluctuation band of the magnetization reversal threshold value Hsw.
Moreover, it is preferable that the magnetization reversal threshold value Hsw is minimized. When the magnetization reversal threshold value Hsw is minimized, there are advantages that the current necessary for data writing can be decreased and the power consumption of, for example, an MRAM chip can be decreased. Furthermore, decrease of the current necessary for data writing is advantageous for circuit design of the MRAM chip because the influence of a galvanomagnetic field and the influence relating to a withstand voltage are decreased.
The rectangle shown in FIG. 49A is ideal as a planar shape of the TMR device 103. However, when the TMR device 103 is further fined, four corners of the TMR device 103 are actually rounded as shown in FIG. 49B and further approach to an ellipse as shown in FIG. 49C. One of the causes is that an isolated island-shaped pattern is formed through, for instance, photolithography every TMR device 103.
Because the planar shape of the TMR device 103 is deviated from an ideal shape, the magnetization reversal threshold value Hsw rises. Moreover, because the planar shape of the TMR device 103 is greatly fluctuated, it is difficult to decrease the fluctuation band of the magnetization reversal threshold value Hsw.